Commit e56d82a1 ("arm64: cpu hotplug: ensure we mask out
CPU_TASKS_FROZEN in notifiers") fixed a long-standing ARM64 bug that
broke single-stepping after a suspend/resume cycle.  Add a kernel
selftest to make sure this doesn't regress or affect other platforms.
Signed-off-by: NGreg Hackmann <ghackmann@google.com>
Signed-off-by: NShuah Khan <shuahkh@osg.samsung.com>